The present invention relates generally to techniques for packaging electronic circuitry, and more specifically to techniques for packaging circuit-carrying substrates interconnected to one or more connector pins of a connector housing or shroud.
Circuit-carrying substrates typically require protection from the environment and an electrical interface to external components and/or systems. In an effort to achieve and also to improve on these two goals, a number of electronic packaging techniques have been implemented. FIG. 1 illustrates a cross-section of one example of a popular conventional electronic package 10 having a circuit-carrying substrate 24 mounted therein and operatively connected to a number of electrical connector pins 20. Package 10 includes a housing 14, typically formed of a plastic resin, affixed to a substrate 12, typically formed of metal, via an adhesive layer 16. The housing 14 defines a connector shroud cavity 18 housing one or more electrical connector pins 20, and the one or more pins 20 extend into a cavity 22 defined by the housing 14. A circuit-carrying substrate 24, typically formed of a ceramic material such as alumina, is affixed to the backplate 12 within the cavity 22 via an appropriate adhesive or epoxy 26, which is typically thermally conductive to provide an adequate heat sink between the substrate 24 and backplate 12. Alternatively, layer 26 may represent a solder connection between the substrate 24 and backplate 12.
The substrate 24 may carry a number of electrical components, and two such components 28 and 30 are illustrated in FIG. 1. Component 28 represents a printed resistor and component 30 represents an integrated circuit mounted to substrate 24 using conventional flip chip technology; i.e., conductive xe2x80x9cbumpsxe2x80x9d are formed on the bond pads of the integrated circuit 30, and the circuit 30 is then mounted to the substrate 24 with its circuit-defining surface facing substrate 30 such that the bumps align with and contact electrically conductive circuit pads or leads defined on the substrate 24. The bumps are thereafter bonded to the circuit pads or leads in a known manner to mechanically and electrically connect the integrated circuit 30 to the substrate 24. Because the mechanical connection between the integrated circuit 30 and the substrate 24 is made only via the bonds between the bumps and the circuit pads or leads, the gap between the integrated circuit 30 and substrate 24 is typically filled with a conventional formable underfill medium 36 that bonds to the circuit-carrying surface of the integrated circuit 30 and to the substrate 24 to thereby secure the mechanical connection therebetween. The underfill process, conventionally carried out via a known capillary underfill technique, is typically carried out before the substrate 24 is mounted to the backplate 12.
The substrate defines thereon a number of bonding locations 32, and wirebonds 34, typically formed of aluminum, are attached between the various bonding locations 32 and corresponding ones of the electrical connector pins 20 extending through the housing 14 into the cavity 22. The cavity 22 is typically filled with a circuit-protecting, pliable, gel-like medium or circuit passivation material 38, and a cap or cover 40 is then mounted to the housing 14 via a suitable adhesive 42. A vent hole 44 is typically provided through the cap 40 to allow for outgassing of one or more of the materials housed within the cavity 22.
Referring to FIG. 2, a flowchart is shown illustrating a typical process 50 for constructing the electronic package 10 of FIG. 1, and process 50 begins at step 52 where any flip-chip mounted integrated circuits 30 carried by the substrate 24 are underfilled as described to secure mechanical connection therebetween. At step 54, the backplate 12 is attached to the housing 14 via adhesive layer 16, and thereafter at step 56 the circuit-carrying substrate 24 is attached to the backplate 12 within the housing cavity 22 via adhesive layer 26. Following step 56, the housing leads or pins 20 are wirebonded to the bonding locations 32 on the substrate 24 at step 58, and thereafter at step 60 the housing cavity 22 is filled with the circuit passivation material 38 and the cover or cap 40 is then mounted to the housing 14 at step 62 via adhesive layer 42.
The electronic package 50 illustrated in FIG. 1 and described hereinabove utilizes complex housing and interconnect designs, and the process of constructing package 50 involves multiple adhesive and formable medium dispense and cure operations. It is accordingly desirable to simplify the package structure and associated manufacturing processes to decrease the cost and complexity, and also to eliminate shortcomings, associated with conventional electronic packages and interconnect configurations.
The present invention comprises one or more of the following features or combinations thereof. A method of forming an overmolded electronic package including a circuit-carrying substrate may comprise the steps of providing a housing defining a cavity therein and defining a connector shroud having a number of electrically conductive leads extending into the cavity, attaching the housing to a backplate, attaching the circuit-carrying substrate to the backplate within the housing cavity, connecting the number of electrically conductive leads to corresponding conductive pads defined on the substrate, filling the cavity with a rigidly formable molding compound and curing the formable molding compound. The connecting step may comprise wirebonding the number of electrically conductive leads to the corresponding conductive pads defined on the substrate to rigidly bond together the backplate, substrate and the housing to form the overmolded electronic package.
The method may further include the step of applying an adhesion promoting layer to a circuit-carrying side of the substrate prior to the filling step, wherein the adhesion promoting layer promotes adhesion between the circuit-carrying side of the substrate and the formable molding compound.
The circuit-carrying side of the substrate may have at least one flip chip mounted thereto with the at least one flip chip and the substrate defining a space therebetween, and the formable molding compound may be configured to flow between the at least one flip chip and the substrate and fill the space prior to the curing step.
The formable molding compound may be configured to exhibit a coefficient of thermal expansion that is near that of the substrate.
Another method of forming an overmolded electronic package including a circuit-carrying substrate may comprise the steps of providing a connector shroud having a number of electrically conductive leads extending therethrough, attaching the connector shroud to one of a backplate and the circuit-carrying substrate, attaching the circuit-carrying substrate to the backplate, connecting the number of electrically conductive leads to corresponding conductive pads defined on the substrate, and overmolding at least the connector shroud and the circuit-carrying substrate with a rigidly formable molding compound to form the overmolded electronic package. The step of attaching the connector shroud may comprise attaching the connector shroud only to the backplate, wherein the overmolding step includes overmolding the connector shroud, the circuit-carrying substrate and the backplate with the rigidly formable molding compound to form the overmolded electronic package. Alternatively, the step of attaching the connector shroud may comprise attaching the connector shroud only to the circuit-carrying substrate, wherein the overmolding step includes overmolding the connector shroud, the circuit-carrying substrate and the backplate with the rigidly formable molding compound to form the overmolded electronic package. Alternatively still, the step of attaching the connector shroud may comprise attaching the connector shroud only to the circuit-carrying substrate, wherein the overmolding step includes overmolding only the connector shroud and the circuit-carrying substrate with the rigidly formable molding compound to form the overmolded electronic package, and wherein the step of attaching the circuit-carrying substrate is executed after the overmolding step.
The connecting step may comprise wirebonding, solder connecting or otherwise electrically and mechanically attaching the number of electrically conductive leads to the corresponding conductive pads defined on the substrate.
The method may further include the step of applying an adhesion promoting layer to a circuit-carrying side of the substrate prior to the overmolding step, the adhesion promoting layer promoting adhesion between the circuit-carrying side of the substrate and the formable molding compound.
The circuit-carrying side of the substrate may have at least one flip chip mounted thereto, the at least one flip chip and the substrate defining a space therebetween, wherein the formable molding compound is configured to flow between the at least one flip chip and the substrate and fill the space.
The formable molding compound may be configured to exhibit a coefficient of thermal expansion that is near that of the substrate.
Yet another method of forming an overmolded electronic package including a circuit-carrying substrate may comprise the steps of attaching the circuit-carrying substrate to a backplate, providing a connector shroud having a number of electrically conductive leads extending therethrough, connecting the number of electrically conductive leads to corresponding conductive pads defined on the substrate, and overmolding at least the connector shroud and the circuit-carrying substrate with a rigidly formable molding compound to form the overmolded electronic package. The overmolding step may include overmolding the connector shroud, the circuit-carrying substrate and the backplate with the rigidly formable molding compound to form the overmolded electronic package. Alternatively, the overmolding step may include overmolding only the connector shroud and the circuit-carrying substrate with the rigidly formable molding compound to form the overmolded electronic package, wherein the step of attaching the circuit-carrying substrate is executed after the overmolding step.
The connecting step may comprise any known lead-connecting process including providing a solder mass between each of the number of electrically conductive leads and the corresponding conductive pads defined on the substrate, and reflowing the solder masses to electrically and mechanically connect the number of electrically conductive leads to the corresponding conductive pads defined on the substrate.
The method may further include the step of applying an adhesion promoting layer to a circuit-carrying side of the substrate prior to the overmolding step, the adhesion promoting layer promoting adhesion between the circuit-carrying side of the substrate and the formable molding compound.
The circuit-carrying side of the substrate may have at least one flip chip mounted thereto, the at least one flip chip and the substrate defining a space therebetween, wherein the formable molding compound is configured to flow between the at least one flip chip and the substrate and fill the space.
The formable molding compound may be configured to exhibit a coefficient of thermal expansion that is near that of the substrate.
Still another method of forming an overmolded electronic package including a circuit-carrying substrate may comprise the steps of providing a connector shroud having a number of electrically conductive leads extending therethrough, connecting the number of electrically conductive leads to corresponding conductive pads defined on the circuit-carrying substrate, overmolding the connector shroud and circuit-carrying substrate with a rigidly formable molding compound while leaving at least partially exposed an underside of the connector shroud and an underside of the circuit-carrying substrate, and attaching a backplate to the undersides of the connector shroud and the substrate after the overmolding step to form the overmolded electronic package.
The connecting step may comprise any known lead-connecting process including providing a solder mass between each of the number of electrically conductive leads and the corresponding conductive pads defined on the substrate, and reflowing the solder masses to electrically and mechanically connect the number of electrically conductive leads to the corresponding conductive pads defined on the substrate.
The method may further include the step of applying an adhesion promoting layer to a circuit-carrying side of the substrate prior to the overmolding step, the adhesion promoting layer promoting adhesion between the circuit-carrying side of the substrate and the formable molding compound.
The circuit-carrying side of the substrate may have at least one flip chip mounted thereto, the at least one flip chip and the substrate defining a space therebetween, wherein the formable molding compound is configured to flow between the at least one flip chip and the substrate and fill the space.
The formable molding compound is configured to exhibit a coefficient of thermal expansion that is near that of the substrate.
A further method of forming an overmolded electronic package including a circuit-carrying substrate having a number of flip-chip circuits mounted thereto may comprise the steps of providing a backplate having a number of thermally conductive posts extending therefrom, attaching the circuit-carrying substrate to the backplate with each of the number of flip-chip circuits mounted to a corresponding one of the number of thermally conductive posts, providing a connector shroud having a number of electrically conductive leads extending therethrough, connecting the number of electrically conductive leads to corresponding conductive pads defined on the substrate, and overmolding the connector shroud, the circuit-carrying substrate and the backplate with a rigidly formable molding compound to form the overmolded electronic package.
The method may further include the step of applying a formable thermally conductive medium between each of the number of flip-chip circuits and a corresponding one of the number of thermally conductive posts.
The method may further include the step of attaching the connector shroud to the circuit-carrying substrate.
The method may further include the step of applying an adhesion promoting layer to a circuit-carrying side of the substrate prior to the overmolding step, the adhesion promoting layer promoting adhesion between the circuit-carrying side of the substrate and the formable molding compound.
Each of the number of flip-chip circuits and the substrate define a space therebetween, wherein the formable molding compound is configured to flow between the number of flip-chip circuits and the substrate and fill the spaces.
The formable molding compound may be configured to exhibit a coefficient of thermal expansion that is near that of the substrate.
The connecting step may comprise any known lead-connecting process including providing a solder mass between each of the number of electrically conductive leads and the corresponding conductive pads defined on the substrate, and reflowing the solder masses to electrically and mechanically connect the number of electrically conductive leads to the corresponding conductive pads defined on the substrate.
These and other features of the present invention will become more apparent from the following description of the illustrative embodiments.